The present invention relates to an apparatus for heat treating a synthetic yarn, such as polyester or polyamide, and especially relates to, but not limited to, an apparatus for heat treating a synthetic yarn which apparatus is installed in a textile machine for false-twisting or drawing and false-twisting the synthetic yarn.
More specifically, the present invention relates to a heat treating apparatus which is suitable for a so called first heater which heat sets twists imparted to a synthetic yarn by a false-twisting device and running back along the synthetic yarn.
In order to enhance the productivity of a false twisting machine or a draw and false twisting machine, it has been proposed to enhance the temperature of a heat treating apparatus for heating set false twists imparted to a synthetic yarn to at least 300.degree. C. (see Japanese Patent Application Laid-open No. Sho 55-16936 or Japanese Patent Application Laid-open No. Sho 57-66145).
Conventionally, when a synthetic yarn is heat treated, i.e., false twists are heat set in a twisting machine or a draw and false twisting machine, a heat treating apparatus of a non-contacting type, wherein the yarn is not directly in contact with the heating member and is passed through a yarn path surrounded by a heating wall, is widely used since the resistance to the imparted false twists is small in such a non-contacting type heat treating apparatus.
However, in such a non-contacting type heat treating apparatus, there are problems that twists are not fully run back along the yarn since the yarn creates vibration or ballooning in the heat treating apparatus, that heat is not transferred well to the yarn since the yarn becomes unstable due to the vibration and that the yarn quality is deteriorated.
The above-described problems become remarkable as the yarn treating speed increases, and therefore, these are the reason why high speed treatment is difficult.
Japanese Utility Model Publication No. Sho 61-42937 discloses an apparatus for heat treating a synthetic yarn at a high temperature more than 300.degree. C. which is provided with yarn path limiting guides by which the yarn is guided along an arc path in order to provide a non-contacting type yarn heating apparatus by which contact of yarn with heating wall due to the ballooning or vibration is prevented and decrease of heat efficiency due to wind loss is prevented.
However, when the temperature of the heater is set at a temperature higher than the melting point of a yarn, for example, of polyester or of polyamide, to be treated but lower than 400.degree. C., during heat treatment of the yarn, the yarn may remain within the heater if the yarn is broken during the yarn treatment, and the remained yarn may be melted and may adhere to the yarn path limiting guides which are disposed within the heater. The melted and adhered material is referred to as "adhesive" hereinbelow in the present specification.
It takes a lot of time until the adhesive is vaporized, in other words, until it changes into a non-liquid state, if the set temperature of a heater is lower than 400.degree. C. Further, if a yarn is threaded again before the adhesive has been vaporized, the material in a liquid state, which is at a high temperature and which has a large heat capacity, adheres to the traveling yarn. Thus, the re-threaded yarn is melted and is broken. Accordingly, it is impossible to thread again while the adhesive in a liquid state is observed on the yarn path limiting guides.
Although the adhesive can be easily removed if an appropriate cleaning article is used, it is a very troublesome operation to manually remove the adhesive from a heater which is heated at a high temperature depending on the locations where the yarn path limiting guides are disposed.
Further, when a false twisted yarn is heat treated at a high temperature, it is usual to set the temperature of the heater so that the temperature of the exit of the heater is equal to a temperature which is required for the yarn. The set temperature of a heater is determined taking into consideration various conditions, such as a yarn speed, yarn thickness (denier), the length of the heater. In this case, it is necessary to set the heater temperature lower than 400.degree. C. depending on the treating conditions. Thus, as described above, there may occur a problem that threading cannot be performed for a long time after breakage of the yarn.
Contrary to this, it has been observed that, for example, in case of polyester yarn, the yarn quality of the obtained yarn is deteriorated, i.e., the crimp characteristic is poor, when the treating time at a high temperature is less than 0.035 min. In other words, it is necessary to heat treat the yarn for a certain time. Accordingly, it cannot be accepted to treat the yarn at an excessively high temperature so that the temperature of the exit of the heater is enhanced while the length of a heater is shortened.
In addition, in a conventional false twisting machine or a draw texturing machine, the length of the heater is set constant in accordance with the machine specification. As described above, the heater length is constant in a conventional machine, and accordingly, the region wherein the treating conditions can be varied is narrow. Thus, the treating conditions, under which the above described disadvantages do not occur, are in a very narrow region.
According to the investigations conducted by the inventors of the present invention, when, for example, a polyester filament yarn was treated, the time which was needed before removal of adhesive depended on the temperatures of the heater as set forth below.
When the temperature of the heater was 370.degree. C., it took about 60 minutes;
450.degree. C., about 2 minutes; and
500.degree. C., about 10 seconds.
Consequently, it has been observed that when the temperature of the heater is set higher than 400.degree. C., the yarn adhered to the yarn path limiting guides can be vaporized in a short time and thus a heater having a self cleaning characteristic can be obtained.